This invention relates to high temperature secondary electrochemical cells and batteries of such cells that can be used as power sources for electric vehicles, storage of off-peak power production and various other applications.
There has been a substantial amount of work in the development of such high temperature, high power electrochemical cells and their electrodes. One group of such cells that show promise include alkali metals or alkaline earth metals and their alloys with more inert materials as negative electrodes. In the positive electrodes of such cells chalogens and transition metal chalogenides are contemplated as active materials. Typical examples include lithium, sodium or calcium and alloys of these active materials with more inert elements such as aluminum, magnesium silicon or boron as a negative electrode materials. In the positive electrode, transition metal sulfides such as iron sulfide, cobalt sulfide, copper sulfide, nickel sulfide and others have been of particular interest. Electrolytes of alkali metal halides and alkaline earth metal halides are typically used in these cells.
High temperature electrochemical cells of these types are illustrated in the following patents:
Artzen, U.S. Pat. No. 4,110,517 shows an electrochemical cell design that employs frangible forms of ceramic materials as electrically insulative cell separators.
Vissers et al, U.S. Pat. No. 4,029,860 illustrates a compartmented or honeycomb structure used as a current collector to support electrochemically active material within an electrode.
Kaun et al., U.S. Pat. No. 4,011,374 describes the use of a resin into which various electrochemically active materials are blended for preparing electrodes.
Mathers et al., U.S. Pat. No. 4,086,396 describes the use of powdered electrically insulative ceramics as separators between electrodes of opposite polarity.
Shimotake et al., U.S. Pat. No. 4,172,926 discloses a secondary electrochemical cell design in which various active material forms suitable for use in high temperature, high specific energy electrochemical cells are described.
Previous secondary electrochemical cells under development have contained flat plate-type electrodes within prismatic or cylindrical housings. Electrically conductive current collectors have extended throughout the flat plate design to be accessible to the active material within the cell. Electrically insulative separator material has extended over and around both flat surfaces between electrodes and over the edge surfaces facing the cell housing. The cells of prismatic shape, although conveniently packed within a battery housing, contain less volume per unit wall area than comparable cylindrical structures, consequently they generally exhibit an increased weight per unit of energy storage capacity. Such flat plate electrode structures are generally prepared by pressing operations that require separate loading and pressing steps for each electrode or electrode separator member.
Previous cylindrical cells have included central pin electrodes of for instance lithium aluminum alloy and an annular electrode of for instance FeS surrounding the central pin. A porous ceramic separator of electrically insulative material is positioned between the electrodes. Cells of this type have the shortcomings of small cell capacity and limited power capability. Increased electrode diameters and thicknesses to increase capacity decreases interelectrode surface and thus power for a given weight. Alternatively, the use of very elongated or a large number of small diameter cells presents cumbersome packaging and connection problems.
Therefore, in view of the foregoing electrochemical cell designs and procedures it is an object of the present invention to provide an improved electrochemical cell with electrodes of cylindrical design.
It is a further object to provide an electrochemical design in which use of electrically insulative separator material is in general restricted to between electrode surfaces of opposite polarity.
It is a further object of the present invention to provide an electrochemical cell containing a plurality of electrode elements of tubular or pin shape to permit their fabrication by extrusion and other continuous processes.